In general, the amount of air provided to a combustion engine is proportionally related to an amount of power that the engine can provide. The power can be supplied as rotational shaft energy to a variety of devices, including vehicles such as automobiles. The engine power is related to its output shaft rotations per minute (RPM) and the torque that shaft is providing. In order to have varying output powers at a given engine RPM, the output shaft torque must vary. The output shaft torque is a function of many variables, but it is largely related to the amount of air entering the engine.
An air boosting system allows the engine to consume more air, thus resulting in the ability to make more torque at the output shaft. One such boosting system is a supercharger, which is a positive displacement air pump that may comprise parallel lobed rotors or offset screw-type rotors. Another type of supercharger is a centrifugal supercharger with a central impeller. A supercharger may provide air or other gaseous matter to an internal combustion engine.
The supercharger may be combined with airflow valves to provide the exact amount of air required to the engine. Because superchargers are generally designed for a fixed volume of air, a bypass valve may also be included. The bypass valve is opened when the full amount of air flowing through the supercharger is not required by the engine. The excess air mass is then allowed to recirculate and enter the inlet of the supercharger again. Any excess air being recirculated still requires energy to pump, and thus decreases the overall efficiency of the boosting system.
Prior art systems have used fixed pulley designs having a pulley attached to a rotating crank shaft of an engine and to a rotational shaft of a supercharger. As engine RPMs increase, and thus the engine's demand for air, the fixed pulley allows the supercharger's rotors to spin faster to provide additional air. The pulley typically sets a fixed ratio between engine RPMs and the supercharger RPMs. While the fixed pulley system allows for the advantage of varying air supply, the air supplied is not always the optimal amount. In addition, the use of a fixed ratio results in a system where either the engine or the supercharger or both cannot be used to the full extent of its rated operational range, resulting in wasted capacity.